Wave slap loading on FPSO bows : research report 324

Abstract

The Schiehallion Floating Production, Storage and Offloading (FPSO) barge suffered wave impact damage to its bow in a storm in November 1998. The impact was a horizontal force applied to near vertical plating and is referred in this report as a wave slap (to distinguish it from wave slap from approximately vertical relative velocities causing impact pressures on the bottom or flared bow). This is a report of model tests and related studies that were undertaken in Glasgow (in what is now the Department of Naval Architecture and Marine Engineering of the Universities of Glasgow and Strathclyde) to understand the problem and provide design guidance. A Glasgow EPSRC-LINK project proposal had already been submitted to research steep wave and impact loads on FPSOs and BP had agreed that Schiehallion could be used for this research. BP decided to provide additional funding to model test/study Schiehallion in greater detail and HSE provided funding to study a tanker (Loch Rannoch, the shuttle tanker for the Schiehallion field) with a more conventional bow shape. Also as a consequence of the Schiehallion damage, a Joint Industry Project, which later became an EU framework 5 project, was started. The Authors of this work also took part in the SAFEFLOW project and there was a considerable exchange of information and ideas between the two projects. The results presented here are complementary to the SAFE-FLOW results and both were used in the derivation of the final SAFE-FLOW design guidance for flat and curved bows. This work is confined to curved bow forms. This report starts, in Section 2, by considering the nature of waves that might cause bow impact damage and how to generate them experimentally. Section 3 describes the model test procedures that were used. Section 4 describes the experimental results. Section 5 describes the results of some simplified calculations that were undertaken to provide a better understanding of the results and that might be use as part of a wave slap prediction method. Section 6 describes how a simplified methodology for calculating design bow forces on curved bow plating was derived from the experiments and calculations. This report does not propose safety factors to use in conjunction with the design forces. However, reliability analysis was conducted as part of the SAFE-FLOW project to enable safety factors to be recommended